It has been a common practice in the welding machine industry to build welding machines with custom tooling as an integral part of the welding machine. In this practice, especially in connection with spot welding machines, each machine is dedicated to the manufacture of a particular part and is not useable for manufacture of other parts. The working area of such a dedicated machine includes an attached assembly of fixtures and tools specifically made, located and adjusted to produce the parts to which the machine is dedicated. The entire machine, from heavy frame to built-in precision fixtures is treated as capital equipment on the financial books of the purchaser. When the parts produced by the dedicated machine are no longer needed, the entire machine is generally scrapped.
There has been a longstanding need in the industry to overcome the disadvantages which accompany the practice of using dedicated welding machines such as the economic loss from scrapping the entire machine when the tools and fixtures are no longer usable because of wear and tear or because of termination of production of the part to which the machine is dedicated. A general objective of this invention is to provide a solution to the problem of economic loss associated with dedicated machines by extending the useful life of those parts of the machine which are not dedicated to a particular product. That part of a given machine, except for the dedicated fixtures and tooling, is herein sometimes referred to as the "base operating machine" whereas the dedicated fixtures and tooling are herein referred to as a "tooling module".
In the prior art, the Henry U.S. Pat. Nos. 4,473,734 and 4,594,494 granted Sep. 25, 1984 and Jun. 10, 1986, respectively, describe a base machine which is adapted to receive interchangeable welding modules. These patents describe an arrangement wherein the base machine is provided with a welding head and a foot treadle actuating device for the upper electrode. Welding current is supplied in the base machine through conductors connected to a conductive base member and to the welding head. The welding electrodes receive welding current through a conductive plate on the module and a movable contact in the welding head.
In Muller et al. U.S. Pat. No. 5,093,977 granted Mar. 10, 1992, a welding machine is described which is adapted for processing differently shaped workpieces with a controlled tool changing capability for quick change of the set of tools. In this system, a central work station is provided with a workpiece holder. More than one tool frame is mounted on the machine and each tool frame may be moved from one station to another. When the processing of the workpiece has been completed by a selected tool frame at the central work station, the processed part may be conveyed out of the station. If other processing operations are to be carried out on the same workpiece or if the processing of a workpiece of a different shape is desired, another tool frame is moved into the central work section after the previous tool frame has been moved out. The processing of the workpiece is accomplished by the substituted tool frame.
It is a general object of this invention to provide a modular welding machine which overcomes certain disadvantages of the prior art.